Effects of mixed cropping on the population abundance of Aphis gossypii Glover and coccinellids on chilli
J.L. Chong, A.B. Idris and M.N. Mohamad RoffA
School of Environmental and Natural Resources Sciences, Faculty of Science and Technology, National University of Malaysia, 43600 Bangi, Selangor, Malaysia.
A MARDI Research Station Jalan Kebun, PO Box 186, GPO, 41720 Klang, Selangor, Malaysia.
The effects of combinations of several crops planted with chilli (Capsicum annuum) on the population abundance of the aphid, Aphis gossypii Glover and coccinellids (Coccinella transversalis Fab. and Harmonia octomaculata Fab.) were assessed. Six crop combinations (treatments) were tested, namely CCCCCCCC, MCMCMCMC, MCOMCOMC, MCEMCEMC, MCOEMCOE and MCEOMCEO (M - maize, C - chilli, O - okra and E - eggplant). The numbers of alate and apterate A. gossypii were significantly different (P <0.05) among treatments. The CCCCCCCC treatment had a significantly higher (P <0.05) number of alate aphids than the other treatments except the MCMCMCMC. However, there was no significant difference (P >0.05) in the number of apterate aphids in the CCCCCCCC with that of MCOMCOMC and MCEMCEMC treatments.
The lower canopy level of chilli had a significantly higher number (P <0.05) of apterate aphids when compared to the upper or middle canopy levels. The numbers of coccinellid eggs per chilli plant were not significantly different between treatments (P >0.05) but there was a significant difference between chilli canopy levels (P <0.05) with a higher number of coccinellid eggs found on the lower canopy level compared to the upper or middle canopy. However, the numbers of adult and larval coccinellids were significantly higher (P <0.05) in the CCCCCCCC treatment than in the other crop treatments with the exception of MCEMCEMC. In contrast to aphids, the numbers of adults and larval coccinellids were significantly higher (P <0.05) in the middle canopy of chilli plant of the CCCCCCCC, MCEOMCEO and MCOMCOMC treatments. This suggests that the effect of predatory coccinellids on aphids could not be separated from factors such as aphid density and crop mixtures.
Plant Protection Quarterly (2004) 19 (3) 90-95.